It applies through the UNFCCC admission system and waits. The secretariat states plainly that at current resource levels the assessment can take six to seven years from application to an answer.
That number is the single most useful fact on this subject and the one least often said out loud. If your organisation is not already admitted, observer status is not a route to COP31. It is a route to a COP in the 2030s.
The requirements are otherwise straightforward: independent legal personality, certified non-profit status, at least one full accounting year of operation, and recent evidence of competence in climate matters. Branches of other bodies, for-profit companies, local governments and political parties are excluded. Once admitted, a body registers delegates conference by conference rather than reapplying.
The realistic path for 2026 is to be nominated by an organisation that is already admitted. Most admitted observers have more badge allocation than people, and many will consider a nomination for someone bringing substance to their programme.